1. Field of the Invention
The present invention relates to a torque detecting apparatus for an electric steering apparatus for use in a vehicle, and more particularly to an improvement in the torque detecting apparatus for detecting the relative rotational displacement of input and output shafts by converting it into an axial displacement.
2. Related Background Art
There are already known various structures for converting the relative rotation between an input shaft and an output shaft into an axial displacement (for example by a screw, a cam or a lever) and detecting said displacement in a housing. However, such conventional structures have been associated with drawbacks such a loss in detection due to many frictional parts involved, susceptibility to the influence of mechanical precision, rigidity or play due to the limited range of axial displacement, or lack of durability due to the abrasion of mechanical parts. Also such structures will become unacceptably bulky or expensive if such drawbacks are to be rectified.
Japanese Utility Model Laid-Open Nos. 59-72529 and 59-195535 disclose a structure provided on the outer periphery of one of the input and output shafts for converting the relative rotational displacement between said shafts into the oscillating motion of an oscillating lever which is further converted into a linear displacement of an axially slidable member.
The above-mentioned torque detecting apparatus, being designed to move the slidable member by enlarging a small displacement of the input and output shafts by means of the oscillating lever, is subject to the influence of play among the component parts, and is associated with the drawbacks of frictional loss, insufficient durability, insufficient rigidity etc.
As explained above, it has not been possible, in the conventional torque detecting apparatus, to achieve a high detecting ability and a long service life with a simple structure.